Gas turbines are widely used in industrial and power generation operations. A typical gas turbine may include a compressor section, a combustor downstream from the compressor section, and a turbine section downstream from the combustor. A working fluid such as ambient air flows into the compressor section where it is compressed before flowing into the combustor. The compressed working fluid is mixed with a fuel and burned within the combustor to generate combustion gases having a high temperature, pressure, and velocity. The combustion gases flow from the combustor and expand through the turbine section to rotate a shaft and to produce work. The combustion gases are then exhausted from the turbine section. In particular gas turbine designs, an exhaust gas recovery system may be positioned downstream from the turbine section.
The compressed working fluid typically contains an excess quantity of oxygen relative to the amount of oxygen required to support the combustion process. As a result, flame temperatures within the combustor may be elevated, thereby increasing thermal stresses within the combustor and/or the turbine section of the gas turbine. In addition, elevated flame temperatures may produce various undesirable emissions, including but not limited to, nitrous oxides (hereinafter NOx), and may also produce other inert components such as nitrogen and water vapor within the exhausted combustion gases.
Typical hydrocarbon fuels used to power modern gas turbines generally include natural gas and oil. However, the supply of hydrocarbon based fuels is generally limited as a non-renewable resource. As a result, high-hydrogen content fuels such as synthetic gas (herein referred to as “syngas”) have been developed as an alternative to the hydrocarbon based fuels. One issue with burning high-hydrogen content fuels, as with burning hydrocarbon based fuels within modern gas turbines, is that undesirable levels of thermal NOx are produced during the combustion process. In addition, the exhaust gases resulting from burning high-hydrogen based fuels contain large concentrations of water vapor.
Various methods are known in the art for reducing the flame temperature and/or the production of NOx within the combustor. One known method includes decreasing the oxygen content of the compressed working fluid prior to combustion by capturing at least a portion of the combustion exhaust gases flowing from the turbine section which have a lower oxygen level than the compressed ambient air entering the compressor, and recirculating the exhaust gas into the compressor and/or into the combustor. As a result, the high oxygen content of the compressed working fluid may be diluted with the low oxygen content exhaust gases, while still providing sufficient oxygen in the working fluid to the combustor in order to support combustion. Other known methods for decreasing the flame temperature and/or reducing NOx production include injecting various diluents such as water or steam into a combustion zone within the combustor.
Although known methods for reducing flame temperatures within a gas turbine are somewhat effective, the allowable levels of emissions such as, but not limited to, NOx that may be emitted by a gas turbine continue to be heavily regulated. Therefore, an improved system and method for further reducing flame temperatures and/or emissions such as NOx within a gas turbine, in particular in gas turbines that burn high-hydrogen fuels would be useful.